Mac computers have always been non-standard computers, meaning that they had their own kind of hardware components and software. Only in 2006 did Apple realize that it’s much better to let others develop components and choose the best ones for your products in the end.
This is how Apple computers (aka Macs) became almost 100% IBM PC compatible, but unfortunately they use only one manufacturer’s (Intel) processors to date. The future promises big changes, because AMD is now capable of building whole computer systems, or at lest the most important parts. AMD currently makes processors, graphics cards and motherboard chipsets for its own processors, so Intel may be only the second choice for future Macs, because Intel ignored this part of the market (graphics cards and motherboard chipsets with integrated GPU).
AMD’s new 890 series platform represents a very serious competition for the current Intel-Nvidia solution for Apple laptops and desktops. Being able to use on-board and discrete graphics cards in Crossfire mode or PowerXpress mode makes AMD’s products superior. To make a long story short, Mac computers are slowly becoming 100% IBM PC compatible for maximum compatibility.
Mac computer accessories are not yet universal, because Apple did adopt some measures to reject some manufacturers when it comes to accessories. One of the main reasons may be the protection of the Apple brand. Shiny new Apple MacBook laptops with any random cheap plastic accessories is not an image Apple wants to see.
Try to imagine a MacBook Pro near a standard white plastic keyboard:

I think we can all agree that original Apple Mac computer accessories are the way to go:
Although it may be a little expensive ($500), these Bowers & Wilkins MM-1 speakers (recommended by Apple) really offer a great experience:

They look great near the iMac or any Apple screen and computer. Unfortunately an external power supply is needed, that adds to the practically non-existent wires, but the sound quality is really good. The total power is just under 10Watts and the speakers reproduce sounds between 38Hz and 22Khz exceptionally.
For Mac desktops and laptops with white exterior, there’s a new accessory available right from Apple’s on-line store:
The 500GB G-DRIVE is just another 5400RPM 2.5” laptop hard drive put in an appropriate Apple-friendly chassis. It costs $140, a price that’s comparable to other manufacturer’s product prices. This little storage device also adds another annoying cable on your desk, but it could be worse if it would require an additional power supply instead of getting all the necessary power right from the USB 2.0 port.
Another interesting recently added Mac computer accessory is a combination of the traditional memory card reader and the USB hub:
The Moshi Universal Media Reader is very practical, because it doesn’t take away your last free USB port, but it gives you an additional port instead. The special compartment for the USB cable makes sure you always have the cable with you, although a retractable cable would have been a better solution. Costing $35 it doesn’t exceed the standard Apple accessory pricing range.